Cephalosporin antibiotics

ABSTRACT

The invention provides new fluorinated cephalosporin antibiotics and methods of preventing or treating infection, particularly mastitis in ruminants, using these antibiotics, and veterinary and pharmaceutical formulations comprising these antibiotics.

CROSS REFERENCE

This application claims the benefit of U.S. Provisional Application No. 60/069,655, filed Dec. 12, 1997, and Provisional Application No. 60/083,646, filed Apr. 30, 1998.

BRIEF SUMMARY OF THE INVENTION

This invention relates to new fluorinated cephalosporin antibiotics and to formulations comprising, and methods of using, these antibiotics to control susceptible pathogens. The invention particularly relates to veterinary formulations and to methods for preventing or treating mastitis in a mammal with a fluorinated cephalosporin of this invention.

Mastitis is a serious problem, especially in the dairy industry. It is an inflammation of the udder caused by a number of different pathogens, including Staphylococcus species and Streptococcus species. There are, however, difficulties in treating mastitis effectively while still meeting the needs of the dairy industry. The agent used must be effective against the pathogen or pathogens causing the mastitis, must not adversely affect the animal being treated, and must be quickly cleared from the animal's system so that the milk it produces may be safe for subsequent use.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides a new group of fluorinated cephalosporin compounds of formula I:

wherein

R^(a), R^(b), R^(c), R^(d) and R^(f), independently, are H, F or a C₁-C₆ alkyl-(Z)_(n)- group having at least one fluorine substituent;

X is O or S;

Y is S, O, or —CH₂—;

Z is O, S, —SO—, or —SO₂—;

m and n independently are 0 or 1;

and

R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substitute selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy;

or a physiologically acceptable salt thereof; provided that:

1) at least one of R^(a), R^(b), R^(c), R^(d) or R^(f) is other than hydrogen; and

2) when X and Y are S and R^(b) or R^(c) is F, one of the remaining R^(a), R^(b), R^(c) R^(d) or R^(f) is other than hydrogen.

The term “C₁-C_(n)-alkyl” refers to a straight or branched chain alkyl group having the designated number of carbon atoms. Examples include methyl, ethyl, isopropyl, n-pentyl, and the like.

The term “halo” refers to chloro, iodo, bromo or fluoro.

The formula I esters, i.e. those compounds wherein R¹ is other than hydrogen or a salt form, act as pro-drugs. Thus, these compounds are converted in vivo to the corresponding free acid that has the desired activity. Certain Formula I esters are preferred. These esters include the pivaloyloxymethyl, acetoxymethyl, methoxymethyl, acetonyl, 1-(acetyloxy)ethyl and phenacyl.

Physiologically acceptable salts of the formula I compounds are also part of this invention. These salts include alkali-metal salts, e.g., sodium, potassium, etc., alkaline-earth metal salts, e.g., calcium, magnesium, etc., and salts with organic bases, such as organic amines, e.g., benzathine, pyridine, triethylamine, tripropylamine and triisopropylamine, etc. The triethylamine and sodium salts are particularly preferred salts.

The formula I compounds are active both in vitro and in vivo against various pathogenic organisms. In one aspect, they are active against certain pathogens that cause mastitis in mammals, particularly in ruminants. A special benefit of the formula I compounds is that they are active at levels such that they may provide improved control of mastitis over products currently used in the dairy industry.

This invention provides, therefore, a method of preventing or treating mastitis in a mammal that comprises administering to the mammal an amount of a formula I compound that effectively prevents or treats the mastitis. This method is particularly useful for preventing or treating mastitis in a ruminant.

The formula I compounds are especially useful for preventing or treating mastitis in cattle, goats and sheep. In one embodiment of this invention, the formula I compound is administered as the animal is lactating (“wet cow” therapy). In this embodiment the milk will be discarded until the mastitis has been successfully treated and the drug has cleared the animal, i.e., the drug is no longer present in the milk. The compounds of this invention may also be used for “dry cow” therapy, that is when administration occurs after lactation, and the animal will thereafter be managed as a dry cow with no further milking until the next parturition. In still another aspect, the formula I compound can be used prophylactically by administering it to a non-lactating animal, such as a nulliparous heifer, in the period prior to parturition.

The formula I compounds can be administered by a variety of methods, such as intramuscularly, subcutaneously, intravenously, intranasally, orally or by intramammary infusion. When used for preventing or treating mastitis, they are preferably administered by intramammary infusion.

It is understood in the art that the amount of formula I compound administered should be the amount that is effective to control the particular pathogen or pathogens in question. In addition, the type, size and condition of the host being treated must be taken into consideration. For example, when controlling a pathogen responsible for mastitis, the dose will vary depending on the type and size of the ruminant being treated.

As an illustration, when treating mastitis in cows, amounts of from about 10 to about 1000 milligrams per quarter are generally effective to control the mastitis. Doses of about 50 to 300 mg per quarter are preferable; and doses of about 100 to 200 mg per quarter are most effective. In goats, on the other hand, amounts of from about 10 to about 100 milligrams per half are generally sufficient; doses of about 10 to 30 mg per half are preferred; and a dose of 20 mg per half is most preferred. An effective amount may also be achieved by multiple dosings.

This invention also provides a veterinary formulation comprising a formula I compound and one or more physiologically acceptable carriers. The veterinary formulations of this invention are particularly useful for preventing or treating mastitis in a mammal, especially a ruminant. Preferred ruminants are cattle and goats.

A pharmaceutical formulation comprising a formula I compound and a pharmaceutically acceptable carrier is another aspect of the invention. These pharmaceutical formulations are useful for treating a bacterial infection in a mammal, especially a human.

The formula I compounds can be formulated for veterinary or pharmaceutical administration according to methods understood in the art. When the compound is to be used in a veterinary formulation for preventing or treating mastitis, the formulation is preferably one that can be administered by intramammary infusion. For this type of infusion, the compound may be formulated in an oily base, e.g., a vegetable oil such as peanut oil or a non-vegetable oil such as mineral oil. The formulation may include a thickening agent and optionally also a surfactant.

When a formula I compound is to be administered to a mammal for the treatment of other types of infections, it may be preferable to administer it in a pharmaceutical formulation comprising one or more pharmaceutically acceptable excipients. The preparation of such formulations is also understood in the art. See, for example, Remington the Science and Practice of Pharmacy, (Mack Publishing Co., Easton, Pa., 1995).

In preparing a pharmaceutical formulation or a veterinary formulation other than for intramammary infusion, the formula I compound is usually mixed with an excipient, diluted by an excipient or enclosed within a carrier that can be in the form of a capsule, sachet, or other container. When the excipient serves as a diluent, it can be a solid, semi-solid, or liquid material that acts as a vehicle, carrier or medium for the active ingredient. Thus, the compositions can be in the form of tablets, pills, powders, lozenges, sachets, cachets, elixirs, suspensions, emulsions, solutions, syrups, aerosols (as a solid or in a liquid medium), ointments, soft and hard gelatin capsules, suppositories, sterile injectable solutions and sterile packaged powders.

During the preparation of the formulation, it may be necessary to mill the active compound to provide the appropriate particle size prior to combining it with the other ingredients. If the active compound is substantially insoluble, it ordinarily is milled to a particle size of less than 200 mesh. If the active compound is substantially water soluble, the particle size is normally adjusted by milling to provide a substantially uniform distribution in the formulation, e.g., about 40 mesh. When the compound is to be used in a formulation for intramammary infusion, it is preferable that the particle size be less than 100 microns and even more preferable that it be about 10 microns.

Examples of suitable carriers, excipients and diluents include lactose, dextrose, sucrose, sorbitol, mannitol, starches, gum acacia, calcium phosphate, alginates, tragacanth, gelatin, calcium silicate, microcrystalline cellulose, polyvinylpyrrolidone, cellulose, water, syrup, and methyl cellulose. The formulations can additionally include: lubricating agents such as talc, magnesium stearate, and mineral oil; wetting agents; emulsifying and suspending agents; preserving agents such as methyl- and propylhydroxybenzoates; sweetening agents; and flavoring agents. The compositions of the invention can be formulated so they provide quick, sustained or delayed release of the active ingredient after administration to the host by procedures known in the art.

For oral administration, the compound can be admixed with carriers and diluents and molded into tablets or enclosed in gelatin capsules.

Other aspects of this invention are processes for preparing a formula I compound. A preferred process for preparing a formula I compound comprises reacting a 3-[(5-methyl-1,3,4-thiadiazolyl)thiomethyl]-7-aminocephalosporanic acid, or a salt or ester thereof, with an acid halide of formula II:

wherein R^(a), R^(b), R^(c), R^(d), R^(f), X and m are as defined supra, and halo is Cl, Br, F or I, to give the formula I compound. This invention also provides a compound of formula I when made by this process.

The following examples illustrate the compounds, processes, methods and formulations of this invention.

EXAMPLE 1

Step 1: Preparation of 1b

Thionyl chloride [8.85 g (5.4 mL), 74.3 mmol] was added to acid 1a (15.2 g, 62.0 mmol) in a 25-mL round-bottom flask. The mixture was heated to reflux (where it became a colorless solution) and maintained there for 1 hr. The solution was cooled, and the excess thionyl chloride was removed on a rotary evaporator at 25 mBar. The remaining solution was distilled at 0.25-0.3 mBar at 56-60° C. to give 14.9 g of 1b as a colorless liquid (92% yield).

Step 2: Preparation of Compound 1

Cephalosporin nucleus 1c (6.54 g, 19.0 mmol) was dissolved by suspending it in H₂O (200 mL) and adding satd. aqueous K₃PO₄ (13 mL). The resulting solution was cooled to 0° C., and acid chloride 1b (4.95 g, 19.0 mmol) was added dropwise over a 1-hr period. K₃PO₄ was also added periodically to keep the pH at about 8. The clear orange solution that resulted was acidified to pH 1 with 1N HCl, filtered and extracted with EtOAc (3×150 mL).

The organic extracts were stirred for 1 hour with activated carbon; the carbon was removed by filtration; and the solution was then evaporated under vacuum to give 9.42 g of an off-white solid. The solid was suspended in diethyl ether and filtered to give 4.81 g of 1, m.p. 93°-100° C. (slow melt); MS=568.8;

Anal.: Calcd. C, 40.14; H, 2.30; N, 9.85. Found C, 40.37; H, 2.26; N, 9.65.

EXAMPLES 2-10

Using analogous procedures to those described in Example 1, a number of illustrative Formula I compounds (Y=S and R¹=H) were prepared. Table 1 summarizes these compounds and certain of their physical characteristics.

TABLE 1 Illustrative Formula I Compounds^(a) Compound R^(a) R^(b) R^(c) R^(d) R^(f) X m MW MP Mass Spec 2 H H CF₃ H H S 1 562.638 159° C. 562 (dec) 3 F F F F F S 1 584.592 101-105° C. 585 4 H H CF₃SO₂ H H S 1 626.703 213° C. 627 (dec) 5 F F CF₃ F F S 1 634.6 116-120° C. 634.8 (dec) 6 F F F F F — 0 552.526 180° C. 553.3 (dec) 7 H H CF₃O H H 0 1 562.568 113-115° C. 563.2 8 H H F H H 0 1 496.564 163° C. 497.3 (dec) 9 F H F H F 0 1 532.545 146° C. 533.1 (dec) 10 H F H F H 0 1 514.552 156° C. 515.2 (dec) ^(a)R¹ = H; Y = S

EXAMPLE 11

Large Scale Preparation of Compound 1

Step 1: Preparation of 1b

Thionyl chloride [71.3 g (43.7 mL), 599 mmol] was added in one portion to the acid 1a (116 g, 479 mmol) in a 250-mL round-bottom flask with stirring. There was little if any gas evolution. The flask was fitted with a condenser and a gas inlet adaptor and heated to reflux under N₂. The reaction mixture became stirrable after 15 min. Heating was continued for about 2 hr, until there was no further gas outflow. The excess thionyl chloride was removed by evaporation under vacuum; then the reaction mixture was distilled at 0.15 mBar at 59° C. to return 110.9 g of 1b as a colorless liquid (89% yield).

Step 2: Preparation of Compound 1

Water (1 L) was added to a 2-L round-bottom flask containing nucleus 1c (73.3 g, 213 mmol). The resulting suspension was cooled to 0° C.; the pH of the solution was adjusted to pH 8 by dropwise addition of saturated K₃PO₄ (113 mL). Acid chloride 1b (55.5 g) was added dropwise over a 2-hr period. During that addition, the pH was maintained at pH 7-8 by adding K₃PO₄ (sat.) in 5-mL portions. [Total amount of K₃PO₄ added as buffer during acid chloride addition was ca. 55 mL].

The solution was allowed to warm slowly to room temperature (about 1 hr) and then filtered over a filter aid (Celite). The filter aid was rinsed with water and then with EtOAc (EtOAc was periodically added to the suction flask during the filtration to prevent foaming). The filtrate was poured into a 4-L separatory funnel; EtOAc (750 mL) was added, followed by HCl (1N, ca. 750 mL) to bring the solution to pH 1. After extraction, the separated aqueous phase was re-extracted with EtOAc (2×750 mL).

Decolorizing carbon (10 g) was added to the combined EtOAc extracts. The mixture was stirred for 30 min and filtered; the filtrate was evaporated under vacuum to give a beige solid. This solid was suspended in diethyl ether to give a thick white slurry. The slurry was evaporated under vacuum to give a light yellow solid, which was dried under vacuum overnight to give 107 g of 1 as a light-yellow solid (88% yield).

EXAMPLE 12

Table 2 summarizes the minimal inhibitory concentrations (MIC's) at which illustrative formula I compounds and cephalothin inhibit certain microorganisms associated with mastitis, such as Staphylococcus aureus 10092 (Newbould strain).

TABLE 2 Comparison on In vitro Activity of Formula I Compounds and Cephalothin vs. Staphylococcus aureus and Streptococcus sp MIC^(a) vs. Compound S.aureus S.aureus S.aureus S.aureus Streptococcus Streptococcus Streptococcus Strepcococcus No. ATCC 29213 174 C 10092 F1C uberis 150 L uberis 166 L agalactiae dysgalactiae 1 0.25 0.25 0.25 0.5 0.25 0.25 0.25 0.125 2 0.25 0.125 0.125 0.25 0.125 0.125 0.125 0.0625 3 0.125 0.0625 0.625 0.125 £0.0078 0.0156 0.0156 0.0156 4 0.0625 0.0312 0.0312 0.125 £0.0078 £0.0078 0.0156 £0.0078 5 0.0625 0.0625 0.0625 0.125 0.0156 £0.0078 0.0156 0.0625 6 0.125 0.125 0.125 0.25 0.0625 0.0156 0.0625 0.0312 7 0.312 0.312 0.312 0.0625 0.0156 0.0078 0.0312 £0.0078 8 0.312 0.0312 0.0312 0.0312 0.0312 0.0312 0.0312 0.0312 9 0.125 0.0625 0.125 0.125 0.0625 0.0625 0.0312 0.125 10  0.0312 0.0312 0.0312 0.0312 0.0312 0.0156 0.0156 0.0312 Cephalothin 0.25 0.25 0.125- 0.25 0.125 0.0625 0.125 0.0615- 0.25 0.125 ^(a)Incubated at 37° C. overnight

The formula I compounds are also active against certain Gram-negative species. Table 3 shows the MIC's of Compound 1 against several Gram-negative species.

TABLE 3 Comparison of In vitro Activity of Compound 1 and Cephalothin against Gram-Negative Organisms MIC^(a) Compound Organism 1 Cephalothin pasteurella multocida 108E (bovine) 0.25 0.5 pasteurella multocida ATCC 12945 0.25 0.25 pasteurella multocida 1051 (swine) 0.25 0.25 pasteurella multocida 10,102 0.25 0.5 (bovine) Pasteurella haemolytica 114F 8 1 (bovine) Pasteurella haemolytica 128K 4 0.5 (bovine) Pasteurella haemolytica 129R 4 1 (bovine) Salmonella typhimurium ≦128 4 Escherichia coli ≦128 8 ^(a)Incubated at 37° C. overnight

EXAMPLE 13 Efficacy of Formula I Compounds in an Induced Staphylococcus aureus Mastitis Model in Lactating Goats

Sixteen lactating goats were selected based on the absence of Staphylococcus aureus in pre-challenge milk cultures. Maintenance ration was provided to the animals throughout the study. The goats were milked twice each day using a portable goat milker.

Milk samples were collected during the morning milking. One day prior to challenge, milk culture samples were collected from each half of the test animals to determine if there was a pre-existing infection. Additionally, a sample was collected from each half for Somatic Cell Count (SCC) determination. A milk culture sample and a sample for SCC were collected from each half 24 hours post-challenge and on Days +4 to +6, +8, +11, +13, and +15.

Udder scoring was performed during each milking wing table:

Severity Score Description 1 Normal milk - no udder swelling 2 Normal milk - udder swelling 3 Abnormal milk - little or no udder swelling 4 Abnormal milk and udder swollen, tender, or hot. Acute clinical mastitis. 5 Acute clinical inastitis with systemic involvement.

General health observations and body temperature were recorded once a day following milking during the challenge and treatment periods.

Milk samples were submitted for analysis for SCC using an electronic somatic cell counting system.

Milk culture samples were assayed for bacterial culture by plating 1.0 mL and 0.1 mL of the milk sample directly onto duplicate blood agar plates. Additionally, dilutions 10⁻¹ of the milk sample were plated. Plates were incubated overnight at 37° C.

Staphylococcus aureus 10092 (Newbould) was used as the challenge strain. The challenge culture was grown in Tryptic Soy Broth (TSB) from a lyovial stock overnight (16 hours) at 37° C. TSB (100 mL) was inoculated with 1 mL of the overnight culture and incubated at 37° C. with shaking for 4 hours. The culture was centrifuged at 9000 rpm for 10 minutes at 10° C.; supernatant was removed and the pellet was resuspended in phosphate buffered saline (PBS). Optimum O.D. reading at 650 nm was approximately 0.035. A 10-fold dilution series was prepared with saline to determine the CFU/mL, plating 10⁻⁵, 10⁻⁶, and 10⁻⁷ dilutions onto duplicate blood agar plates. The 10⁻⁷ dilution (approximately 10 CFU/mL) was used for the challenge material, yielding a challenge of 50 CFU/half with a 5-mL infusion.

Sixteen goats were used for the trial. During a one day pre-challenge period, milk samples were collected and temperatures were taken during the morning milking. Milk/udder evaluations were documented during the morning and afternoon milkings.

Staphylococcus aureus 10092 was infused into both halves in each of the goats. The goats were challenged following the morning milking and milked in the afternoon on the day of challenge. The challenge inoculum volume was 5 mL/half containing approximately 50 CFU S. aureus.

For the 24 hr post-challenge period milk samples were collected during the morning milking, and milk/udder evaluations made during the morning and afternoon milking.

Treatment was started at 36 hours post-challenge. Milk samples were collected for culture and SCC 24 hours post-challenge, prior to the morning milking, and the treatment period started following the afternoon milking.

Eight halves (4 goats) each were treated for 2 consecutive milkings 12 hours apart, following milking. Each designated compound was formulated in peanut oil with 45 mmoles of compound per 5 g of formulation to give approximately 25 mg/5 mL dose.

Following treatment, the goats were milked and observed for 15 days. Milk samples were collected on Days +4 to +6, +8, +11, +13, and +15 to determine if the infection had cleared.

Establishment of mastitis was determined by bacterial culturing, severity of udder scoring, somatic cell count results, and body temperature.

On Days +2 to +6, milk samples were collected for a calorimetric assay to determine whether the antibiotic was still present in the milk.

Table 4 summarizes the activity of typical formula I compounds in this assay.

TABLE 4 In vivo Efficacy of Formula I Compounds vs. Staphylococcus aureus-Induced Mastitis in Goats Compound % Bacteriologic Cures 1 71 2 83 3 50 4 71 5 33 6 60 7 100 8 100 9 83 10 33

EXAMPLE 14 Efficacy of Compound 1 in Mastitis in Cows

Compound 1 was administered to lactating cows in three trials using methods analogous to those used in the goat model described in Example 13. A total of 43 quarters were treated with Compound 1, and 36 quarters were treated with cephapirin (Cefa-Lak). Both compounds were administered at 450 mmoles/quarter/dose for two doses. Compound 1 effectively treated 27 out of 43 quarters for an overall cure rate of 63%, whereas cephapirin effectively treated 18 out of 36 quarters for an overall cure rate of only 50%. 

I claim:
 1. A compound of the formula

wherein m is 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof.
 2. A compound of the formula

wherein R^(a), R^(b), R^(c), R^(d) and R^(f), independently, are H, F or a C₁-C₆ alkyl-(Z)_(n)-group having at least one fluorine substituent; Z is O, S, —SO—, or —SO₂—; n is 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof; provided that: 1) at least one of R^(a), R^(b), R^(c), R^(d) , or R^(f) is other than hydrogen; and 2) when R^(b) or R^(c) is F, two of the remaining R^(a), R^(b), R^(c), R^(d) , or R^(f) are other than hydrogen.
 3. A compound of the formula

wherein R^(a), R^(b), R^(c), R^(d) and R^(f), independently, are H, F or a C₁-C₆ alkyl-(Z)_(n)-group having at least one fluorine substituent; Z is O, S, —SO—, or —SO₂—; n is 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C_(l)-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof; provided that: 1) at least one of R^(a), R^(b), R^(c), R^(d) , or R^(f) is other than hydrogen; and 2) when R^(b) or R^(c) is F, one of the remaining R^(a), R^(b), R^(c), R^(d) , or R^(f) is other than hydrogen.
 4. A compound of the formula

wherein R^(a), R^(b), R^(d) and R^(f) are H; R^(c) is CF₃; Z is O, S, —SO—, or —SO₂—; m and n independently are 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof.
 5. A compound of the formula

wherein R^(a), R^(b), R^(c), R^(d) and R^(f) are F; Z is O, S, —SO—, or —SO₂—; m and n independently are 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof.
 6. A compound of the formula

wherein R^(a), R^(b), R^(d) and R^(f) are H; R^(c) is CF₃SO₂; Z is O, S, —SO—, or —SO₂—; m and n independently are 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof.
 7. A compound of the formula

wherein R^(b) and R^(d), independently, are H, F or a C₁-C₆ alkyl-(Z)_(n)-group having at least one fluorine substituent, and R^(c) is F; Z is O, S, —SO—, or —SO₂—; n is 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof.
 8. A compound of the formula

wherein R^(b) and R^(d) , independently, are H, F or a C₁-C₆ alkyl-(Z)_(n)-group having at least one fluorine substituent, and R^(c) is a C₁-C₆ alkyl-(Z)_(n)-group having at least one fluorine substituent; Z is O, S, —SO—, or —SO₂—; n is 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C_(l)-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof.
 9. A compound of claim 7 wherein R^(b) and R^(d) and F.
 10. A compound of the formula

wherein R^(a), R^(b), R^(c), R^(d) and R^(f), independently, are H, F or a C₁-C₆ alkyl-(Z)_(n)-group having at least one fluorine substituent; Z is O, S, —SO—, or —SO₂—; n is 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof; provided that: 1) at least one of R^(a), R^(b), R^(c), R^(d), or R^(f) is other than hydrogen; and 2) when R^(b) or R^(c) is F, two of the remaining R^(a), R^(b), R^(c), R^(d), or R^(f) are other than hydrogen.
 11. A method of preventing or treating mastitis in a mammal that comprises administering an effective amount of a compound of formula I:

wherein R^(a), R^(b), R^(c), R^(d) and R^(f), independently, are H, F or a C₁-C₆ alkyl-(Z)_(n)-group having at least one fluorine substituent; X is O or S; Z is O, S, —SO—, or —SO₂—; m and n independently are 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof; provided that: 1) at least one of R^(a), R^(b), R^(c), R^(d) or R^(f) is other than hydrogen; and 2) when X is S and R^(b) or R^(c) is F, one of the remaining R^(a), R^(b), R^(c), R^(d) or R^(f) is other than hydrogen.
 12. A method of claim 11, wherein the formula I compound is one wherein m is 1 and X is O.
 13. A method of claim 11, wherein the formula I compound is one wherein m is 1 and X is S.
 14. A method of claim 11, wherein the formula I compound is one wherein R^(a), R^(b), R^(c), R^(d) and R^(f) are F.
 15. A method of claim 1 wherein the mammal is a ruminant.
 16. A compound of claim 3 wherein R^(a), R^(c) and R^(f) are F.
 17. A method of claim 15 wherein the ruminant is a cow.
 18. A method of claim 15 wherein the ruminant is a goat.
 19. A compound of the formula

wherein R^(a), R^(b), R^(c), R^(d) and R^(f), independently, are H, F or a C₁-C₆ alkyl-(Z)_(n)-group having at least one fluorine substituent; Z is O, S, —SO—, or —SO₂—; n is 0 or 1; R is

and R¹ is H, C₁-C₆-alkyl, phenyl or benzyl, each of which may optionally have up to three substituents selected from halo, C₁-C₄-alkoxy, phenyl, NO₂, C₁-C₆-alkanoyl, benzoyl, or C₁-C₆-alkanoyloxy; or a physiologically acceptable salt thereof; provided that: 1) at least one of R^(a), R^(b), R^(c), R^(d) , or R^(f) is other than hydrogen; and 2) when R^(b) or R^(c) is F, one of the remaining R^(a), R^(b), R^(c), R^(d), or R^(f) is other than hydrogen. 